The present invention relates to a vacuum actuator and, more particularly, to a vacuum actuator having a vacuum control solenoid valve integrally fixed to the wall surface of a casing of the actuator.
It is known to integrally fix a vacuum control solenoid valve to the wall surface of an actuator. In the known vacuum actuators, however, a control pressure chamber for accomodating a valve member and a solenoid device for controlling said valve member are stacked in the axial direction of the actuator rod and on the upper surface of the case. Since the solenoid device having a considerable weight is disposed at an upper part of the actuator, the weight center or centroid of the vacuum actuator is positioned at a considerable distance from the mounting surface of the vacuum actuator, i.e. from the bottom surface of the vacuum actuator. Therefore, if the vacuum actuator is fixed to a portion subjected to a vibration, the solenoid device makes a rocking motion due to the vibration to impart a large repetitional force to the fixing portion of the vacuum actuator due to the inertia caused by the vibratory rocking motion, often resulting in a breakdown or loosening of the fixing portion.
The vibratory force due to the vibratory rocking of the solenoid device is applied also to the joint between the case of the actuator and the case of the valve, as well as to the joint between the valve case and the solenoid device, to cause a separation at these joints or cracking in the resin portion around these joints, resulting in various troubles such as a leakage of vacuum from the valve case, dropping of the solenoid device and so forth.
These problems are particularly serious in the case of vacuum actuators mounted on automobile engines due to the vigorous vibration inherent in these engines.